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Let’s temper our expectations on the Covid-19 vaccine

Doctors most knowledgeable about vaccine development warn that, however promising a vaccine may seem now or months from now, premature release can do far more harm than good

By DR. EDUARDO GONZALES

I do not doubt that we will eventually develop a safe and effective vaccine for Covid-19. The signs point to that—the virus does not mutate at a fast rate, some of the promising vaccines are already undergoing clinical trials, governments are cutting the red tape that is associated with vaccine approval, and manufacturing deals are already being signed. 

But let’s temper our expectations because, despite all this good news, a safe and effective Covid-19 vaccine is unlikely to be available for mass immunization anytime soon. Furthermore, contrary to what most people think, a vaccine will not eradicate the virus overnight, if it eradicates the virus at all.

It takes time to produce a new vaccine

It takes years to produce a safe and effective vaccine. The fastest vaccine ever developed was for mumps. It took four years. Experts are not starting from scratch when it comes to the Covid-19 vaccine. The SARS-CoV-2 virus is a relative of the SARS and MERS viruses, and a lot of work has already been done on the development of a vaccine for these two infections that can be put into good use in the development of a Covid-19 vaccine. Still, the most optimistic estimates place a Covid-19 vaccine as one to two years away.

Vaccine development is a complex and painstaking multi-stage process. It starts with identifying the antigens (parts or weakened strains of a virus) that will be incorporated in the candidate vaccine. Then, tissue-culture or cell-culture and animal testing are performed to find out if the candidate vaccine will produce immunity.

This is followed by three stages of clinical testing. Phase one entails testing for safety and immunogenicity in normal adults (less than 100 people), phase two entails testing for immunogenicity and safety in special populations (hundreds of human subjects), while phase three, which can include thousands of test subjects, continues to measure the safety (rare side effects sometimes don’t appear in smaller groups) and effectiveness of the candidate vaccine.

After the clinical trials, the candidate vaccine is submitted for regulatory review and approval. It is only after it is approved by regulatory authorities (e.g., FDA), is a vaccine manufactured.  

A vaccine will not eradicate the virus overnight

No vaccine is 100 percent effective. The flu vaccine is only 65 percent effective while the measles vaccine is 95 percent effective. Even if the Covid-19 vaccine turns out to be as highly effective as the flu vaccine, as many as five percent of people who get the vaccine can still get sick with Covid-19. But a vaccine need not be 100 percent effective to achieve herd immunity. Herd immunity refers to the protection from a contagious disease that is conferred on an entire population because enough of its people are immune to (i.e., they do not get or spread) the disease. The percentage of the population which must be immunized to achieve herd immunity varies for each disease. For highly contagious diseases, the required figure is high. Measles requires 90 to 95 percent immunization coverage to achieve herd immunity, polio is 80 to 85 percent, while for Covid-19, that remains to be determined.

The measles vaccine has been around since the late ’60s and despite an effective vaccine and all-out immunization campaigns, as a country, we have not attained herd immunity from measles. Periodic outbreaks of the disease still occur, killing hundreds of Filipino children annually.

To date, the only pathogenic virus we have eradicated worldwide is the smallpox virus. In 1958, armed with a safe and effective vaccine, the World Health Organization (WHO) started a global immunization campaign against smallpox. Yet it was only in 1979, more than 20 years later, that the WHO declared the world as free from smallpox.

All indications, therefore, point to the fact that, even in the best-case scenario, the virus will stay with us for a long, long time. But the situation is not hopeless, because we can adopt certain lifestyle changes that can contain the spread of the virus and prevent it from infecting us. And I’m pretty certain that an antiviral drug that can alleviate if not cure Covid-19 will become available soon.


Source: Manila Bulletin (https://mb.com.ph/2020/07/14/lets-temper-our-expectations-on-the-covid-19-vaccine/)

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