{"id":7515,"date":"2021-01-06T00:47:54","date_gmt":"2021-01-06T07:47:54","guid":{"rendered":"https:\/\/sanjhisoch.com\/english\/?p=7515"},"modified":"2021-01-06T00:47:54","modified_gmt":"2021-01-06T07:47:54","slug":"explained-how-safe-is-it-to-switch-between-types-of-covid-19-vaccines-reduce-or-delay-doses","status":"publish","type":"post","link":"https:\/\/sanjhisoch.com\/english\/explained-how-safe-is-it-to-switch-between-types-of-covid-19-vaccines-reduce-or-delay-doses\/","title":{"rendered":"Explained: How Safe is it to Switch Between Types of Covid-19 Vaccines, Reduce or Delay Doses"},"content":{"rendered":"
The proposals have generated fierce debate among scientists. Here is the rationale behind, and criticism of, these alternative strategies.<\/strong><\/h6>\n

Sanjhi Soch Beauro \u2013<\/strong>Britain and other nations are considering ways to stretch scarce supplies of\u00a0COVID-19<\/span><\/span>\u00a0vaccines, including by delaying second doses, reducing dose sizes and switching vaccine types between the first and second shots.<\/p>\n

The proposals have generated fierce debate among scientists. Here is the rationale behind, and criticism of, these alternative strategies:<\/p>\n

WHY DELAY THE SECOND DOSE?<\/h4>\n

 <\/p>\n

In clinical trials, companies tested specific doses of their vaccines at precise time intervals to generate evidence showing how well they work. All\u00a0COVID-19<\/span><\/span>\u00a0vaccines approved, so far, are designed to teach the immune system to recognise and defend against the virus with a first dose, and then provide a second booster dose to reinforce that lesson.<\/p>\n

Faced with a fast-spreading pandemic and new, more transmissible\u00a0coronavirus<\/span><\/span>\u00a0variants, some countries are hoping to widen immunisation by giving some protection to as many people as possible with a first dose, and delaying second doses.<\/p>\n

Maximising the number of people who have partial immunity \u201cshould reduce the number of severe\u00a0COVID-19<\/span><\/span>\u00a0cases and thus alleviate the burden on hospitals\u201d, said Michael Head, a global health expert at Britain\u2019s University of Southampton.<\/p>\n

For a FACTBOX on countries\u2019 dosing intervals, click here:<\/p>\n

\n

WHAT ABOUT SWITCHING BETWEEN COVID VACCINES?<\/h4>\n

 <\/p>\n

Mixing or switching between\u00a0COVID-19<\/span><\/span>\u00a0vaccines is largely driven by the same aim \u2013 vaccinating as many people as possible as the pandemic still rages.<\/p>\n

Giving a priming dose of one vaccine and a booster dose of another offers flexibility to offer whichever shots are available, rather than holding shots back so individuals always get both doses of the same vaccine.<\/p>\n

\n

HAVE THESE STRATEGIES BEEN TESTED IN RIGOROUS TRIALS?<\/h4>\n

 <\/p>\n

No.<\/p>\n

None of the late-stage\u00a0COVID-19<\/span><\/span>\u00a0vaccine trials compared these dose-sparing strategies or the effects of mixing vaccine types, said Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine (LSHTM).<\/p>\n

Officials have cited limited evidence from trials that the Pfizer\/BioNTech, the Oxford University\/AstraZeneca and the Moderna vaccines all confer some protection against\u00a0COVID-19<\/span><\/span>\u00a0after the first dose.<\/p>\n

Britain\u2019s MHRA health regulator said on Dec. 30 it had found an 80% success rate for the Oxford\/AstraZeneca vaccine when two full doses are administered, three months apart, higher than the average that the developers themselves had found.<\/p>\n

The UK government\u2019s vaccine advisory committee said on Dec. 31 that the Pfizer\/BioNTech vaccine conferred 89% protection from two weeks after the first dose, and that for the Oxford\/AstraZeneca vaccine \u201cthe evidence shows that the initial dose \u2026 offers as much as 70% protection against the effects of the virus\u201d. It did not give detailed data.<\/p>\n

Moderna reported its vaccine was 80% protective after one dose, with efficacy peaking two weeks after the first shot.<\/p>\n

But there is no long-term evidence that any of these vaccines will offer lasting immunity based on just one dose, or how effective they will be if the second dose is delayed.<\/p>\n

BioNTech and Pfizer warned on Monday they had no evidence their vaccine would continue to be protective if the second dose was given more than 21 days after the first.<\/p>\n

Evans said that ideally \u201cit is safest and most cautious\u201d to use vaccines in conditions exactly matching those of their trials, but added: \u201cIn the real world, this is never so.\u201d<\/p>\n

Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, told CNN on Friday the United States was unlikely to delay giving second doses.<\/p>\n

\u201cWe\u2019re going to keep doing what we\u2019re doing,\u201d he said.<\/p>\n

Likewise, scientists have raised concerns over the idea of mixing two different types of vaccines. Some experts speculate that, because all of the vaccines target the same outer \u201cspike\u201d protein of the virus, they could work together to train the body to fight off the virus.<\/p>\n

But there is no evidence this approach will work.<\/p>\n

There is literally zero data. It has not been tested, or if it has been tested, the data have not been made available,\u201d said John Moore, a professor of microbiology and immunology at Weill Cornell Medical College in New York.<\/p>\n

\n

WHAT ABOUT REDUCING THE AMOUNT OF VACCINE IN EACH DOSE?<\/h4>\n

 <\/p>\n

In the United States, some health officials are considering offering half doses of Moderna\u2019s vaccine to individuals aged 18 to 55. There is some clinical trial data backing this strategy.<\/p>\n

Moncef Slaoui, chief adviser to the U.S. vaccine programme Operation Warp Speed, told CBS on Sunday that evidence from a Moderna trial showed the half dose induced an \u201cidentical immune response\u201d to the higher 100 microgram dose in adults aged 55 and under. He said the U.S. government was discussing the issue with Moderna and regulators.<\/p>\n

Slaoui said he believed injecting half of the volume of vaccine was \u201ca more responsible approach that would be based on facts and data\u201d.<\/p>\n

Several U.S. scientists agreed, but noted the data was not publicly available. \u201cIt\u2019s very fuzzy. I want to see that data,\u201d said Eric Topol, a genomics expert and director of the Scripps Research Translational Institute in La Jolla, California.<\/p>\n

SO ARE THESE STRATEGIES SAFE? AND WILL THEY WORK?<\/h4>\n

 <\/p>\n

It\u2019s not clear.<\/p>\n

While there is no scientific evidence on the impact of delaying\u00a0COVID-19<\/span><\/span>\u00a0vaccine doses, some experts believe it could be safe to wait and the potential payoff in protecting a larger swath of the population may be worth it.<\/p>\n

Others aren\u2019t so sure.<\/p>\n

\u201cThere\u2019s just no data,\u201d said Ian Jones, a professor of virology at Britain\u2019s Reading University.<\/p>\n

The British Society of Immunology said in a statement on Monday that delaying a second dose by eight weeks \u201cwould be unlikely to have a negative effect on the overall immune response\u201d. It added that it would not expect any extra safety risks from the delay beyond the potential increased risk of disease during the interim between doses.<\/p>\n

Some scientists also said that while there was no evidence to support the strategy of mixing vaccine doses from different manufacturers \u2013 a method known as heterologous prime-boost \u2013 evidence from other vaccines provided some reassurance.<\/p>\n

\u201cBased on previous studies which combine different vaccine types, a combination of the AstraZeneca and Pfizer vaccines is likely to be safe,\u201d said Helen Fletcher, a professor of immunology at LSHTM.<\/p>\n

Topol called the mix-and-match strategy \u201ca big mistake\u201d with \u201cunpredictable\u201d results \u2013 including the potential for adverse reactions or a significant drop-off in efficacy. \u201cIt makes no sense whatsoever,\u201d he said.<\/p>\n

Some worry about safety issues, particularly with delaying the second dose for several weeks. The gap could allow time for the virus to evolve and develop resistance to the vaccine.<\/p>\n

Weak antibody protection could also increase the risk of having an abnormal immune response \u2013 such as antibody-dependent enhancement \u2013 when people encounter the real virus, Topol said.<\/p>\n

\n

HOW PRACTICAL IS IT TO PROLONG DOSING TIME SCHEDULES?<\/h4>\n

 <\/p>\n

Extending the interval poses adherence risks, raising the chance people may forget or fail to return for a second dose.<\/p>\n

It also increases the length of time during which they are less than optimally protected, and it could make it harder for health authorities to keep track of who has had which vaccine, when, and how often.<\/p>\n

Given these risks, immunology and public health experts say clear communication is imperative to ensure people understand that although dosing schedules may be subject to change, two\u00a0COVID-19<\/span><\/span>\u00a0vaccine doses are needed to give the best protection.<\/p>\n","protected":false},"excerpt":{"rendered":"

The proposals have generated fierce debate among scientists. Here is the rationale behind, and criticism of, these alternative strategies. Sanjhi Soch Beauro \u2013Britain and other nations are considering ways to stretch scarce supplies of\u00a0COVID-19\u00a0vaccines, including by delaying second doses, reducing dose sizes and switching vaccine types between the first and second shots. The proposals have […]<\/p>\n","protected":false},"author":2,"featured_media":7516,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[4],"tags":[],"yoast_head":"\n\n\n\n\n\n\n\n\n\n\n\n\t\n\t\n\n\n\n\n\t\n