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 The results appear to surpass those seen with Merck & Co Inc's pill
molnupiravir, which was shown last month to halve the likelihood of
dying or being hospitalized for COVID-19 patients also at high risk
of serious illness.
Full trial data is not yet available from either company.
Pfizer said it plans to submit interim trial results for its pill,
which is given in combination with an older antiviral called
ritonavir, to the U.S. Food and Drug Administration as part of the
emergency use application it opened in October.
The combination treatment, which will have the brand name Paxlovid,
consists of three pills given twice daily.
The planned analysis of 1,219 patients in Pfizer's study looked at
hospitalizations or deaths among people diagnosed with mild to
moderate COVID-19 with at least one risk factor for developing
severe disease, such as obesity or older age.
It found that 0.8% of those given Pfizer's drug within three days of
symptom onset were hospitalized and none had died by 28 days after
treatment. That compared with a hospitalization rate of 7% for
placebo patients. There were also seven deaths in the placebo group.
Rates were similar for patients treated within five days of symptoms
- 1% of the treatment group was hospitalized, compared with 6.7% for
the placebo group, which included 10 deaths.
Antivirals need to be given as early as possible, before an
infection takes hold, in order to be most effective. Merck tested
its drug within five days of symptom onset.
"We saw that we did have high efficacy, even if it was five days
after a patient has been treated ... people might wait a couple of
days before getting a test or something, and this means that we have
time to treat people and really provide a benefit from a public
health perspective," Annaliesa Anderson, head of the Pfizer program,
told Reuters.
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The company did not detail side
effects of the treatment, but said adverse
events happened in about 20% of both treatment
and placebo patients.
"These data suggest that our oral antiviral
candidate, if approved by regulatory
authorities, has the potential to save patients’
lives, reduce the severity of COVID-19
infections, and eliminate up to nine out of ten
hospitalizations,” Pfizer Chief Executive Albert
Bourla said in a statement.
Infectious disease experts stress that
preventing COVID-19 through wide use of vaccines
remains the best way to control the pandemic,
but only 58% of Americans are fully vaccinated
and access in many parts of the world is
limited.
Pfizer's drug, part of a class known as protease
inhibitors, is designed to block an enzyme the
coronavirus needs in order to multiply.
Merck's molnupiravir has a different mechanism
of action designed to introduce errors into the
genetic code of the virus. Merck has already
sold millions of courses of the treatment, which
was approved this week by U.K. regulators, to
the United States, the U.K. and others.
Britain said earlier this month it had secured
250,000 courses of Pfizer's antiviral.
 Pfizer is also studying whether its pill could
be used by people without risk factors for
serious COVID-19 as well as to prevent
coronavirus infection in people exposed to the
virus.
(Reporting By Deena Beasley; editing by Grant
McCool)
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