Some vaccines help nations exit pandemic faster than others

WASHINGTON • With hundreds of millions of people now vaccinated against Covid-19, the coronavirus pandemic should begin to die down in places where a large chunk of the population has been inoculated. But that is not happening everywhere.

Instead, two paths are emerging: In countries such as Israel, new Covid-19 cases are declining as more people are vaccinated, while in other places like the Seychelles - which has fully inoculated more of its population than any other nation - infections continue to increase or even reach new highs.

One reason could be the different types of vaccine being used.

Evidence derived from the expanding global inoculation roll-out indicates that the messenger RNA (mRNA) shots developed by Pfizer-BioNTech and Moderna are better at stopping people from becoming contagious, helping reduce onward transmission - an unexpected extra benefit as the first wave of Covid-19 vaccines were intended to stop people from becoming very sick. Other vaccines, while effective in preventing acute illness or death from Covid-19, appear not to have this extra perk to the same degree.

"This will be an increasing trend as countries start to realise that some vaccines are better than others," Professor Nikolai Petrovsky from the College of Medicine and Public Health at Flinders University in South Australia said.

While the use of any vaccine "is still better than nothing", he added, some doses "may have little benefit in preventing spread, even if they reduce the risk of death or severe disease".

Studies of millions of people in Israel vaccinated with the Pfizer-BioNTech shot show that the mRNA doses prevented more than 90 per cent of asymptomatic infections - those who contract the virus but show no symptoms. That is important, said Dr Raina MacIntyre, an epidemiologist at the University of New South Wales in Sydney, because a vaccine's ability to stop asymptomatic infection "is the determinant of whether or not herd immunity is possible".

Herd immunity is typically achieved when the virus can no longer find any vulnerable hosts in order to keep spreading.

Which vaccines a country can secure could, therefore, affect everything from policy about mask-wearing and social distancing to lifting border restrictions and reviving economies, given the influence that daily case counts have on government decisions. For individuals, it may mean how soon they regain pre-pandemic freedoms.

In Israel, nearly 60 per cent of its population has been vaccinated with the Pfizer-BioNTech vaccine, and the country has gradually lifted restrictions as new cases fell to fewer than 50 a day, from more than 8,000 at the start of this year.

The results provide further evidence of the surprise efficacy of the new mRNA shots; the coronavirus pandemic is the first time this vaccine technology is being widely used. They work by delivering genetic codes that instruct the human body to make proteins of the virus that in turn stimulate an immune response.

The existing mRNA shots require ultra-cold storage, limiting their accessibility in countries with poor transport and storage infrastructure.

But the US Food and Drug Administration on Wednesday said the Pfizer-BioNTech vaccine can be stored at refrigerator temperatures for up to a month. It said it made the decision "based on a review of recent data submitted by Pfizer", and will allow vials of the vaccine to be stored at refrigerator temperatures of 2-8 deg C for up to one month. The vials were previously only allowed to be kept at such temperatures for five days.

Still, ultra cold storage requirements is one reason why most countries are relying mainly on non-mRNA shots ranging from AstraZeneca's vaccine to those from Chinese developers Sinopharm and Sinovac Biotech. These more traditional vaccine types have shown efficacy rates of between 50 per cent and 80 per cent in preventing symptomatic Covid-19 in clinical trials, compared with more than 90 per cent for mRNA ones. There is little data regarding their ability to prevent onward transmission, but signs are emerging that it may be much lower.

AstraZeneca pointed to the success of Britain's campaign as evidence of its shot's benefits, though the results include the impact of Pfizer-BioNTech's inoculation. Covid-19 infections in Britain fell by 65 per cent after a first dose of either shot, while household transmissions dropped by as much as 50 per cent. Sinopharm did not respond to queries for this story.

In the Seychelles, the authorities have fully vaccinated about 65 per cent of its population with shots from AstraZeneca or Sinopharm, yet weekly new infections rose rapidly this month, with 37 per cent of those patients having already received their two doses. Among fully inoculated people, around 60 per cent received the vaccine from Sinopharm and the rest got AstraZeneca's shot.

What seems clear is that all the approved doses reduce the incidence of people becoming severely ill or dying from the disease - the primary goal of a vaccine. That takes pressure off hospitals and medical resources. Most new Covid-19 patients in the Seychelles, for example, are only experiencing mild symptoms.

This is a crucial first step for countries without access to mRNA vaccines, said Associate Professor Helen Petousis-Harris, a vaccinologist at the University of Auckland. After using available vaccines to crush the number of severe cases, countries can stamp out remaining infection with shots that curb transmission once they become available, she said.

BLOOMBERG, AGENCE FRANCE-PRESSE